I changed my website ruzzleonline.nl to multisite and everything went great.

The layout of the website was correct except the main menu didn't used the colors specified in Simple CSS lite plugin I was using for that.

When I was in the dashboard of ruzzleonline, I went to the settings from Simple CSS lite plugin and saw that all the colors were correct. I hit save and from that moment my layout of the website is not good anymore.

I don't know how to get it back on track. I network disabled Simple CSS lite plugin, but that had no effect.

I host the website at WPEngine and indeed there is a cache. I cleared it on multisite level and on site level. I was to quick reading your advice, because when I went to permalinks, I saw a real long permalinks activated with year, date etc. etc, so I did change it to only postname again how it was before, saved it. Links are working on the website, but design is still not back.

Before I changed to multisite I had the customize plugin on ruzzleonline.nl installed, I changed that without problems to a child theme, and from there on I changed it to multisite. Don't know if it helps telling this, but at this moment I don know what the problem is, so I just provide you with information.

Willem, I doubt the pagelines-customize plugin being converted to a child theme is the root cause of this, but, let me point out that child themes can be updated by their authors (except for Base Theme), and some things work best in the customize plugin, like hooks. I'd suggest restoring that.

As for the Simple CSS Lite plugin, I'm going to have to defer this to one of my colleagues as I don't know why that would cause any disruption, unless the CSS it writes is not carrying into the multisite environment.

From experience... that was the problem on my Multisite and it took forever to discover until James B [of Pagelines] suggested it. Refresh the sites by visiting them, and it was done. Problem solved. I'm not sure which site you are working on though, so it could be the same problem.